Seats such as more particularly office chairs which comprise a seat portion and a backrest portion frequently have at least two gas spring units for performing at least two different functions such as adjusting the angle of inclination of the seat portion and adjusting the angle of inclination of the backrest portion, to adapt the seat to the respective requirements of the person using same.
In one form of such a seat, as disclosed in European patent No. 0 022 933, the seat comprises a common operating lever for operating the two gas spring units to provide for the respective adjustment functions thereof. In broad terms, the operating lever has a knob or handle at one end, while at its other end, it is mounted pivotably about a vetical axis, so as to move in an at least generally horizontal direction. At a further location spaced from the end remote from the handle end of the lever, the lever is mounted slidably in a horizontal guide slot. The mounting arrangement provides a common pivot point for both horizontal pivotal movement and vertical pivotal movement of the operating lever, and the operating lever can thus describe any pattern or figure in the plane perpendicular to its longitudinal axis, if it is moved with a horizontal pivotal movement and also a vertical pivotal movement, out of its original position. That structure therefore requires an additional guide means for guiding the lever, in the form of a control gate configuration, so that only the pivotal movements required for actuation of the individual gas springs can be performed, thus ensuring that the lever is operated in a well-defined and unambiguous manner.
German laid-open application (DE-OS) No. 33 25 798 discloses a gas spring unit which is designed in particular for adjusting the backrest portion of a chair or the like, which has an operating lever. The operating lever has a handle or gripping portion at one end while at the opposite end it is guided in a slot opening, displaceably both vertically and horizontally, while at a location spaced therefrom, it is mounted slidably in a vertical guide slot and pivotably horizontally about the longitudinal axis of the vertical guide slot.